Load bearing fabric attachment and associated method

ABSTRACT

An attachment structure for a load bearing fabric. The attachment structure includes interfitted inner and outer rings. The outer ring includes a fabric leg  74  carrying a load bearing fabric. The inner ring defines a channel receiving the fabric leg  74 . The inner ring and outer ring are configured to stretch the fabric upon insertion of the fabric leg  74  into the channel. The present invention also provides a method for securing a load bearing fabric to a support structure, generally including the steps of (a) providing an outer ring having fabric leg  74 , (b) attaching a section of load bearing fabric to the fabric leg  74 , (c) providing an inner ring having a channel adapted to receive the leg of the outer ring and (d) installing the outer ring to the inner ring by inserting the leg into the channel, the insertion forcing the fabric down into the channel and stretching the fabric to the desired tension.

This application is a continuation of U.S. patent application Ser. No.09/769,967 filed Jan. 25, 2001, to Coffield et al, now U.S. Pat. No.6,842,959.

BACKGROUND OF THE INVENTION

The present invention relates to load bearing fabric, and moreparticularly to components and methods for securing a load bearingfabric to a support structure.

The use of load bearing fabrics continues to grow dramatically invarious industries, including the automotive, office and home seatingindustries. The term “load bearing fabric” is commonly used to refer toa class of high strength, highly durable textiles that are typicallywoven from elastomeric monofilaments and conventional yarns. Some oftoday's load bearing fabrics have greater strength and durabilitycharacteristics than spring steel and other conventional load bearingmaterials. In addition to their strength and durability characteristics,load bearing fabrics are lightweight and typically have a high modulusof elasticity. Therefore, they are well-suited for use in a variety ofapplications where a strong and durable yet lightweight or elastic loadbearing surface is desired, for example, in seating, cots and wheelchairapplications. Further, because load bearing fabrics are aestheticallypleasing they can and often are exposed during use, for example, as theseat or back of an office chair. This eliminates the need to cover ortrim conventional load bearing surfaces.

One particularly important challenge related to the use of load bearingfabric is the challenge of attaching the fabric to the supportstructure. Although load bearing fabrics have high strength anddurability characteristics, they must be properly attached to thesupport structure to provide an end product with the desired strengthand durability. This task is particularly challenging because it istypically important to attach the fabric to the support structure in astretched or tensioned state. This applies a constant load to theconnection between the fabric and the support structure.

Conventional attachment methods often fail to provide the necessarystrength and durability to withstand the forces applied to the fabric.As a result, the fabric separates from the support structure underconditions that the fabric is otherwise well-suited to survive. In someapplications, the bond itself may fail and in other applications, themethod of attachment may cause the fabric to unravel or separate alongthe periphery of the fabric. Accordingly, there is an ongoing effort todevelop new and improved methods and components for securing the loadbearing fabric to the support structure.

Perhaps the most common use of load bearing fabric is in the furnitureindustry, where load bearing fabrics are used to form the seat and backof task seating, executive chairs and other office chairs. In thefurniture industry, load bearing fabrics are typically secured to asupport structure by an outer ring, often in the form of a peripheralframe. The fabric is first attached to the outer ring and then the outerring is attached to the support structure, such as the seat frame orback frame. In such applications, the challenge is to secure the outerring in a way that provides a strong and durable bond without damagingor promoting unraveling of the fabric. One conventional method foraddressing these issues is to secure the load bearing fabric to an outerring through encapsulation. In general, encapsulation involves themolding of an outer ring in situ about the peripheral edge of thefabric. During the molding process, the material of the outer ring flowsthrough and becomes intimately intersecured with the fabric. The outerring is then secured to the support structure using fasteners or otherconventional techniques and apparatus.

Although encapsulation provides a strong and durable bond, it suffersfrom a number of disadvantages. To provide the chair with a firm seatand back, the fabric must typically be tightly stretched over the chairand back frames. The conventional method for providing the fabric withthe desired amount of stretch is to hold the fabric in a stretchedposition while the outer ring is molded in place about the fabric. Thisoperation involves the use of expensive looms and stretching machinery.The stretching machinery stretches the fabric to the desired position.The stretched fabric is then mounted to the loom, which holds the fabricin the stretched position during the molding process. It may also benecessary to provide molding equipment that is specially configured tooperate while the loom holds the stretched fabric. Further, when themolded outer ring and fabric emerge from the mold, the force of thestretched fabric can cause the outer ring to deform, for example, to bowor “potato chip.” This creates the need to return the outer ring to thedesired shape, typically using additional machinery, prior to attachmentto the support structure. As can be seen, this conventionalencapsulation method requires a relatively complex manufacturing processthat employs expensive looms and stretching machinery.

Another alternative is to mold the outer ring from an elastic orstretchable material so that the outer ring can be stretched after it isintersecured with the fabric. In general, this process involves moldingthe outer ring about the load bearing fabric while the load bearingfabric is in a relaxed state. After the molding process, the outer ringis stretched or expanded to apply the desired tension to the fabric.Although this process provides a marked improvement over the prior art,it requires a separate stretching or expansion step following themolding process.

SUMMARY OF THE INVENTION

The aforementioned problems are overcome by the present inventionwherein a load bearing fabric attachment is provided with an outer ringand an inner ring that are configured such that installation of theouter ring to the inner ring stretches the fabric to the desiredtension. In the preferred embodiment, the inner ring defines a channelopening in a direction substantially perpendicular to the direction ofthe fabric. The outer ring includes a leg that is adapted to be fittedwithin the channel. The fabric is mounted to the leg of the outer ringtoward its lower end, such that a portion of the fabric is forced uponassembly to stretch down into the channel in a direction substantiallyperpendicular to the remainder of the fabric, thereby giving the fabricthe desired tension.

In a more preferred embodiment, the outer ring is substantially L-shapedhaving a first leg that extends substantially in the plane of the fabricand a second leg that extends substantially perpendicularly to the planeof the fabric. The first leg overlies the inner ring and provides theouter ring and inner ring assembly with additional strength and a neatand tidy appearance. The second leg holds the peripheral edge of thefabric and is fitted within the outer ring channel.

In a more preferred embodiment, the location at which the fabric isattached to the second leg of the outer ring is varied about the outerring to control the amount of stretch in the fabric in differentregions. The fabric is preferably attached to the leg throughencapsulation to provide a strong and durable attachment of the fabricto the outer ring.

The present invention also provides a method for attaching a loadbearing fabric to a support structure. The method generally includes thesteps of (a) providing a rigid outer ring for carrying a load bearingfabric, the outer ring having a leg extending substantiallyperpendicularly to the fabric, (b) attaching an unstretched load bearingfabric to the leg of the outer ring, preferably by encapsulation, (c)providing an inner ring having a channel adapted to receive the leg ofthe outer ring and (d) installing the outer ring to the inner ring byinserting the leg into the channel, the insertion forcing the fabricdown into the channel and stretching the fabric to the desired tension.

The present invention provides a simple and effective method forattaching a load bearing fabric to a support structure. Because theouter ring and inner ring are configured to stretch the fabric uponassembly of the two components, the fabric need not be stretched priorto molding or prior to attachment to the outer ring. Further, the amountof stretch is engineered into the inner and outer rings, and need not bedirectly controlled during manufactured and assembly. This reduces thecost and complexity of the manufacturing process. The present inventionalso permits the amount of tension applied to the fabric to vary indifferent directions, for example, between the left/right direction andthe front/rear direction. Accordingly, the present invention providesfor an inexpensive yet strong and highly durable attachment.

These and other objects, advantages, and features of the invention willbe readily understood and appreciated by reference to the detaileddescription of the preferred embodiment and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an office chair incorporating apreferred embodiment the present invention;

FIG. 2 is an exploded perspective view of the seat;

FIG. 3 is a top plan view of the seat outer ring;

FIG. 4 is a side elevational view of the seat outer ring;

FIG. 5 is a sectional view of the seat outer ring taken along line V—Vof FIG. 3;

FIG. 6 is an enlarged view of area A of FIG. 5;

FIG. 7 is a top plan view of the seat inner ring;

FIG. 8 is a sectional view of the seat inner ring taken along lineVIII—VIII of FIG. 7 with portions removed to show portions of itsundersurface;

FIG. 9 is a sectional view of the seat inner ring taken along line IX—IXof FIG. 7;

FIG. 10 is an enlarged view of area B of FIG. 8;

FIG. 11 is an enlarged view of area C of FIG. 9;

FIG. 12 is a sectional view of the seat outer ring and load bearingfabric positioned over the seat inner ring;

FIG. 13 is a sectional view of the seat outer ring and load bearingfabric attached to the seat inner ring;

FIG. 14 is a perspective view of the back outer ring;

FIG. 15 is a perspective view of the back inner ring;

FIG. 16 is top plan view of the assembled back inner ring and back outerring;

FIG. 17 is a sectional view of the assembled back inner ring and backouter ring taken along line XVII—XVII of FIG. 16;

FIG. 18 is a sectional view of an open mold in a first location alongthe ring;

FIG. 19 is a sectional view of a closed mold in a first location alongthe ring; and

FIG. 20 is a sectional view of the mold in a second location along thering.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For purposes of disclosure, and not limitation, the present invention isdescribed in connection with an office chair 10 having load bearingfabric that forms the seat and back of the chair. The present inventionis well suited for use in a wide variety of other applicationsincorporating load bearing fabric. For example, the present invention iswell suited for use with footwear soles, mattresses, cots, wheelchairsand a variety of seating applications outside of office furniture.

An office chair manufactured in accordance with a preferred embodimentof the present invention is shown in FIG. 1, and generally designated10. Referring also to FIG. 2, the office chair 10 includes aconventional base 20 upon which is supported a seat 12 and a back 14.The seat 12 and back 14 each include a load bearing fabric 16 and 18,respectively, that forms the corresponding support surface. The seat 12includes an inner ring 26 that is preferably an integral portion of theseat frame and an outer ring 28 that carries a section of load bearingfabric 16 and is attached to the inner ring 26. Similarly, the back 14includes an inner ring 30 that is preferably an integral portion of theback frame and an outer ring 32 that carries a section of load bearingfabric 18 and is attached to the inner ring 26. In general, the seat 12is manufactured by (a) placing an unstretched section of load bearingfabric 16 in a mold (not shown), (b) molding the outer ring 28 in situabout the periphery of the unstretched fabric 16, (c) fitting the outerring 28 to the inner ring 26, whereby interaction of the outer ring 28and inner ring 26 stretches the fabric 16 to the desired tension, and(d) securing the outer ring 28 to the inner ring 26. The back 14 ismanufactured in accordance with essentially the same process.

With the exception of the load bearing fabric and the associatedattachment components, the office chair 10 is generally conventional.Accordingly, components of the chair 10 not associated with or unique tochair's use of load bearing fabric will not be described in detail. Ingeneral, however, the chair 10 includes a conventional base 20 having afive leg pedestal 21 with casters 23, a support column 25 extendingupwardly from the pedestal and a top plate 22 mounted atop the supportcolumn. The described base 20 is merely exemplary, and it can bereplaced by any of a wide variety of conventional bases as desired. Forexample, the pedestal 21 may be replaced by other conventionalpedestals. If desired, the support column 25 can be a conventionalheight-adjustable column. The seat 12 is mounted to and carried by thetop plate 22, for example, by screws, bolts or other conventionalfasteners. The chair 10 further includes a generally conventional backsupport 24, which is mounted to the top plate 22 to provide a mountingsurface for the back 14.

The attachment structure and manufacturing method of the presentinvention will be described in detail with reference to the seat 12portion of the office chair 10. In the preferred embodiment, the seat 12generally includes an inner ring 26 that is attached to the top plate22, an outer ring 28 that is fitted within and attached to the innerring 26 and a section of load bearing fabric 16 that is affixed to theouter ring 28 (See FIG. 2). Referring now to FIGS. 7–11, the inner ring26 preferably includes an integral seat pan portion 27. The seat panportion 27 is generally convex to provide a void beneath the fabric 16,and is shaped to correspond with the desired seat contours. The seat panportion 27 includes a mounting surface 29 that mounts directly to thetop plate 22. For example, the mounting surface 29 preferably includesscrew bosses (not shown) adapted to receive screws, bolts or otherfasteners (not shown) for securing the seat 12 to the top plate 22 (SeeFIG. 2). Obviously, the seat 12 can be secured to the top plate 22 in avariety of alternative ways. The inner ring 26 extends around theperiphery of the seat pan portion 27 and defines a channel 48 adapted toreceive the fabric leg 74 of the outer ring 28, as described in moredetail below. The channel 48 preferably extends around the entire innerring 26, and, as perhaps best shown in FIGS. 11 and 13, is of sufficientdimension to receive substantially all of the fabric leg 74 of the outerring 28. The inner ring 26 further defines a plurality of locking slots80 in the floor of the channel 48 that receive the corresponding lockingtabs 82 of the outer ring 28 to interconnect the two rings, as describedin more detail below. A locking finger 84 is disposed adjacent to eachslot 80 to lock the outer ring 28 in place within the inner ring 26. Thelocking fingers 84 each include a barb 86 adapted to interlock with acorresponding barb 88 on the locking tabs 82. The locking fingers 84 areformed in the wall of the inner ring 26 and are somewhat flexiblepermitting deflection of the fingers 84 during installation of the outerring 28. If desired, the bottom wall of the channel 48 may also oralternatively define screw clearance holes, screw bosses or otherconventional elements to further or alternatively secure attachment ofthe outer ring 28 within the channel 48. In the preferred embodiment,the inner ring 26 is an integral portion of the seat frame beingintegrally attached to the seat pan portion 27. Alternatively, the seatinner ring 26 can be manufactured as an annular component that isseparate from the seat pan (not shown). If so, the inner ring 26 can beattached to the seat pan or other structural component that is supportedupon the top plate 22 or directly upon the pedestal.

As noted above, the outer ring 28 carries the fabric 16 and interactswith the inner ring 26 to stretch the fabric 16 to the desired tensionupon installation of the outer ring 28 to the inner ring 26. Referringnow to FIGS. 3–6, the outer ring 28 is a rigid, generally peripheralframe defining a central opening 90 over which the fabric 16 issuspended. The outer ring 28 is shaped and contoured to correspond withthe shape and contours of the inner ring 26. The outer ring 28 issubstantially L-shaped in cross section defining a trim leg 76 and afabric leg 74. The trim leg 76 extends in an outwardly direction insubstantial alignment with the fabric 16. The trim leg 76 strengthensthe outer ring 28 and provides the seat 12 with a neat and tidyappearance. The size and shape of the trim leg 76 may vary fromapplication to application, and may be eliminated in some applications,if desired. The fabric leg 74 is a substantially straight leg adapted tobe fitted into the channel 48 of the inner ring 26. The fabric leg 74also carries the peripheral edge of the fabric 16. In the preferredembodiment, the fabric 16 is encapsulated within the fabric leg 74,meaning that the fabric leg 74 is molded about the fabric 16 such thatthe peripheral edge of the fabric 16 is intimately intersecured with thefabric leg 74 during the molding process. Alternatively, the fabric 16can be attached to the fabric leg 74 by mechanical attachments, such asmounting screws extending through a mounting strip (not shown). Asdescribed in more detail below, the insertion of the fabric leg 74 intothe channel 48 causes the fabric 16 to stretch to the desired tension(See FIGS. 12 and 13). By varying the position at which the fabric 16 isattached to the fabric leg 74 the amount of stretch applied to thefabric 16 can be controlled. For example, mounting the fabric 16adjacent to the lower end of the fabric leg 74 will result in a greateramount of stretch while mounting the fabric 16 adjacent to the upper endof the fabric leg 74 will result in a lesser amount of stretch. In thepreferred embodiment, the fabric 16 is attached to the fabric leg 74 insuch a way as to provide substantially more stretch in the left/rightdirection than in the front/rear direction. More specifically, thepreferred embodiment is designed to provide approximately 4.5% stretchin the left/right direction and less than approximately 1% stretch inthe front/rear direction. To provide the desired variation in tension,the fabric 16 is attached lower on the fabric leg 74 along the left andright sides of the outer ring 28 and higher on the fabric leg 74 alongthe front and rear sides of the outer ring 28. The outer ring 28preferably includes an approximately three inch transition portion ineach corner in which the fabric 16 transitions between its differentmounting locations on along the various sides. In the preferredembodiment, the load bearing fabric 16 includes elastic monofilamentsextending in the left/right direction and substantially nonelastic yamsextending in the front/rear direction. As a result, the greater amountof stretch is applied to the fabric 16 in the direction of the elasticmonofilaments.

The outer ring 28 further includes a plurality of locking tabs 82extending downwardly from the lower edge of the fabric leg 74. Thelocking tabs 82 each include a barb 88 and are shaped and positioned tobe snap-fitted into the locking slots 80 of the inner ring 26. Thelocking tab barbs 88 interlock with the corresponding locking fingerbarbs 86 to intersecure the inner ring 26 and outer ring 28. At leastone of the barbs 86 or 88 preferably includes a ramped surface thatcause the locking tabs 82 and/or locking fingers 84 to flex away fromeach other during insertion of the fabric leg 74 into the channel 48.

The load bearing fabric 16 conforms to the desired shape of the seat 12.More specifically, the size and shape of the load bearing fabric 16 ispreselected to accommodate the precise size and shape of the outer ring28. As described in more detail below, the load bearing fabric may beany of wide variety of load bearing fabrics, including polyesterelastomer fabrics. For purposes of this application, the term “fabric”refers to both woven and non-woven materials, including withoutlimitations knit materials. If desired, woven fabrics with welded warpand weft intersections can be used. These fabrics are particularlywell-suited for use in applications in which the material of the outerring is not from the same family of resin as the materials as thefabric. In such applications, the welded intersections permit the outerring 28 to more securely interlocks with the fabric 16. In general, theseat outer ring 28 is molded in place about the fabric 16 so that thematerial of the seat outer ring 28 flows through and entraps the warpsand wefts to provide a secure interconnection between the outer ring 28and fabric 16. Where the resin of the outer ring 28 is from the samefamily as the resin of the fabric 16, the outer ring 28 and the fabric16 adhere to one another. The encapsulation process not only produces astrong bond, but also reduces the likelihood of the fabric unravelingalong its periphery. Although the seat outer ring 28 is preferablyattached to the fabric 16 using encapsulation, the seat outer ring canbe separately manufactured and attached to the fabric using conventionalattachment techniques. For example, the outer ring can be manufacturedfrom two parts that sandwiched the fabric (not shown).

The back 14 of the chair 10 is constructed in accordance withsubstantially the same principles as the seat 12 (See FIGS. 14–17).Although the size and shape of the back 14 differ from those of the seat12, the general components and method of manufacture of the back 14 aresubstantially identical to those of the seat 12. Accordingly, theconstruction and method of manufacture of the back 14 will not bedescribed in detail. Suffice it to say that the back 14 includes a backinner ring 30, a back outer ring 32 and a section of load bearing fabric18. The back inner ring 30 defines a channel 148 and is mounted to theback support 24. Unlike the seat inner ring 26, the back inner ring 30has open center 92, and preferably does not include a seat pan or theequivalent thereof. The back outer ring 32 includes a trim leg 176 and afabric leg 174, and is molded in situ about the fabric 18 while thefabric 18 is in a relaxed state. In the preferred embodiment, thelocation at which the fabric 18 is attached to the fabric leg 174 variesalong the back outer ring 32 and is selected to provide less thanapproximately 1% stretch in the left/right direction and approximately6–7% stretch in the top/bottom direction. To provide the desiredvariation in tension, the fabric 18 is attached higher on the fabric leg174 along the left and right sides of the back outer ring 32 and loweron the fabric leg 174 along the front and rear sides of the back outerring 32. As with seat outer ring 28, the back outer ring 32 preferablyincludes an approximately three inch transition portion in each cornerin which the fabric 18 transitions between its different mountinglocations on along the various sides. As noted above, the load bearingfabric 18 preferably includes elastic monofilaments intersecting withsubstantially nonelastic yarns. In the back 14, the elasticmonofilaments extend in the left/right direction and the yarns extend inthe up/down direction. As a result, the greater amount of stretch isapplied to the fabric 18 in the direction of the substantiallynonelastic yams.

As noted above, the back 14 is mounted to the chair 10 upon back support24. The back support 24 is generally L-shaped having a pair of lowerlegs 100 and 102 that extend substantially horizontally and mount to thetop plate 22, for example, by bolts (not shown). The back support 24further includes a pair of upright legs 104 and 106 that extend upwardlyfrom the lower legs 100 and 102, respectively. A generally U-shapedmounting bracket 108 is disposed at the upper ends of the upright legs104 and 106. The back support 24 is preferably fabricated from metalwith the mounting bracket 108 being welded to the upright legs 104 and106. Alternatively, the back support 24 can be molded or cast as aone-piece unit from a high strength material, such as metals or highstrength plastics. In any event, the mounting bracket 108 is shaped tocorrespond with the inner ring 30 of the back 12, and preferably definesa plurality of spaced mounting holes 110 that permit the inner ring 30to be screwed or bolted to the back support 24 in a conventional manner.

MANUFACTURE AND ASSEMBLY

The base 20, top plate 22 and back support 24 are manufactured usingconventional techniques and apparatus. In the described embodiment, thebase 20 is assembled from a conventional five-leg pedestal 21, casters23 and a conventional support column 25. The pedestal 21, caster 23 andsupport column 25 are preferably premanufactured, and are available froma variety of well-known suppliers. The top plate 22 is configured in aconventional manner to mount to the support column 25 and to supportablyreceive the seat inner ring 26. Similarly, the back support 24 isconfigured as described above to be attached to the top plate 22 and tosupportably receive the back inner ring 30. The top plate 22 and backsupport 24 are preferably fabricated from an appropriate metal, such asan aluminum alloy, but may alternatively be manufactured from othermetals or structural plastics. If desired, a height control, recliner,seat tilt control and other adjustment mechanisms can be incorporatedinto chair 10, for example, into the pedestal 20, the top plate or theback support 24.

The load bearing fabric 16 and 18 is premanufactured and is availablefrom a variety of well-known suppliers. For example, the fabric may bemanufactured from Dymetrol fabric available from Acme Mills of Detroit,Mich.; Pellicle fabric available from Quantum Inc. of Colfax, N.C.;Collage fabric available from Matrix of Greensboro, N.C. or Flexnetfabric available from Milliken of Spartanburg, S.C. The load bearingfabric 16 preferably a welded fabric. The load bearing fabric 16 and 18is cut, preferably using conventional die cutting techniques andapparatus. The size and shape of the fabric 16 and 18 is preselected,such that it assumes the desired tension upon insertion of the outerring into the inner ring. The fabric 16 and 18 preferably includes aperipheral marginal portion 17 that can be held between the base die 64and the cover die 66 to hold the fabric in the desired position withinthe mold.

The molding process will now be described in connection with themanufacture of the seat outer ring 28. Referring now to FIGS. 18–20, themold 60 includes an base die 64 and a cover die 66 that are shaped todefine a mold cavity 62 in the desired shape of the seat outer ring 28.The dies 64 and 66 are shaped to define a parting line 120 adjacent toportion of the mold cavity 62 that forms the fabric leg 74 such that thefabric 16 enters the mold cavity at the fabric leg 74. As noted above,the preferred embodiment provides the fabric 16 with significant stretchin the left/right direction and only minor stretch in the front/reardirection. The location of the parting line 120 will vary along the seatouter ring 28 to encapsulate the fabric 16 within the fabric leg 74 atdifferent locations at various locations in the seat outer ring 28. Asnoted above, this provides the fabric 16 with differing amounts ofstretch in different directions. The base die 64 includes a conventionallifter 65 that grips the peripheral edge of the fabric 16 to hold it inplace during the molding process. FIG. 19 is a sectional view of a firstportion of the mold 60 showing the fabric 16 entering the mold cavity 62near the top of the fabric leg 74. FIG. 19 is representative of theconfiguration of the mold 60 along the front and rear segments of theseat outer ring 28. As a result, the fabric 19 will be provided withrelatively little stretch in the front/rear direction. FIG. 20 is asectional view of a second portion of the mold 60 showing the fabric 16entering the mold cavity 62 toward the bottom of the fabric leg 74. FIG.20 is representative of the configuration of the mold 60 along the leftand right segments of the seat outer ring 28. As a result, the fabric 16will be provided with significantly more stretch in the left/rightdirection than in the front/rear direction. The dies 64 and 66 areconfigured to provide an approximately three inch transition portion inthe corners of the mold cavity 62 where the parting line 120, or theentry point of the fabric 16, transitions between the locations shown inFIGS. 19 and 20. The location of the parting line 120 at various regionsof the seat outer ring 28 will vary from application to application toaccommodate the desired stretch profile for that application. Ifdesired, the cover die 66 can include a conventional steel gasket 67 toaid in preventing the flow of molten material from the mold cavity 62.The gasket 67 can be coated with silicone, urethane or otherconventional materials.

The load bearing fabric 16 is placed in the mold cavity 62 of the mold60 for the seat outer ring 28. The fabric 16 is placed in the moldcavity 62 in a relaxed state with no creases or folds. The fabric 16preferably extends through the mold cavity 62 and is trapped along aperipheral marginal portion by lifter 65 (See FIGS. 19 and 20).Alternatively, the fabric 16 may be trapped directly between the basedie 64 and cover die 66 (not shown) or it may terminate within thecavity (not shown). In the preferred embodiment, the dies 64 and 66define a slight relief 68 inwardly from the mold cavity to preventpotential crushing damage to the fabric 16 inwardly from the outer ring28 when the dies are closed. The relief 68 is, however, small enough toprevent the flow of molten material out of the mold cavity 62 and intothe relief 68. Gasket 67 further aids in preventing the flow of moltenmaterial out of the mold cavity 62 through the parting line 120. Theseat outer ring 28 is then injection molded about the periphery of thefabric 16 using generally conventional molding techniques and apparatus.Suffice it to say that molten material is introduced into the moldcavity 62, where it flows through and, after curing, becomes intimatelyinterconnected with the fabric 16. The seat outer ring 28 is preferablymanufactured from a thermoplastic, such as polypropylene, nylon,polyester, or a thermoset, such as a structural epoxy resin. After theseat outer ring 28 is sufficiently cured, the outer ring/fabric assemblyis removed from the mold, providing a relaxed fabric 16 contained withina rigid outer ring 28. Any peripheral marginal portion 17 can be trimmedfrom the fabric 16 as desired. In applications where a welded fabric isnot used, the outer ring is preferably manufactured from a resinselected from the same family of resins as the fabric 16, such as Hytrel4556 or 5556 available from Dupont, Arnitel EM 440 available from DutchState Mine (“DSM”) of Evansville, Ind. This promotes a strong anddurable bond between the fabric 16 and the outer ring 28.

The seat inner ring 26 is also manufactured using conventional moldingapparatus. The seat inner ring 26 is molded with channel 48 to receivethe seat outer ring 28. The channel 48 is not, however, strictlynecessary and the seat outer ring 28 can be attached to a substantiallyvertical outer surface of the seat inner ring 26 using conventionalfasteners or the like. The seat inner ring 26 is molded with seat panportion 27 and mounting portion 29. The seat inner ring 26 is preferablymanufactured from nylon, polypropylene or PET or other structuralresins, and may be reinforced with glass fibers or other similarreinforcement materials. After it is sufficiently cured, the seat innerring 26 is removed from the mold. A plurality of screw holes (not shown)are drilled into the mounting structure 29 of seat pan portion 27 toreceive screw (not shown) for intersecuring the seat inner ring 26 tothe top plate 22. The number and location of screw holes will vary fromapplication.

The seat outer ring 28 is next mounted to the seat inner ring 26. Ingeneral, the seat outer ring 28 is attached to the seat inner ring 26 byinserting the fabric leg 74 into the channel 48. The seat inner ring 26is inserted into the channel 48 until the locking tabs 82 and lockingfingers 84 interlock to hold the inner ring 26 and outer ring 28together. Alternatively, the locking tabs 82 and locking fingers 84 canbe removed and the inner ring 26 and outer ring 28 can be intersecuredby screws, adhesive or other conventional methods. The outer ring 28 ispreferably inserted into the inner ring 26 using a conventional press(not shown), but can be inserted manually in some applications,depending primarily on the required amount of force. The seat inner ring26 is then secured to the top plate 22, for example, by screws, tocomplete assembly of the seat 12.

As noted above, the back 14 is manufactured and constructed in a mannersimilar to the seat 12. In short, the seat back fabric 18 is cut to thedesired shape, the back outer ring 32 is molded in situ onto the fabric18, the back inner ring 30 is molded, and the back outer ring 32 andfabric 18 are inserted into the back inner ring 30 until the lockingfingers 184 and locking tabs 182 interlock. The back inner ring 30 andouter ring 32 are preferably manufactured using molds (not shown) thatare substantially similar to the molds used in manufacturing the seatinner ring 26 and outer ring 28. A plurality of screw holes 134 areformed in the inner ring 30, preferably either integrally molded withthe inner ring 30 are drilled into the inner ring 30 after the innerring 30 is molded. The assembled back 14 is then mounted to the backsupport 24 in a generally conventional manner, for example, using screwsextending through screw holes 134 in the inner ring 30 and the mountingholes 110 in the back support 24.

The above description is that of a preferred embodiment of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theappended claims, which are to be interpreted in accordance with theprinciples of patent law including the doctrine of equivalents. Anyreference to claim elements in the singular, for example, using thearticles

a,

an,

the

or

said,

is not to be construed as limiting the element to the singular.

1. A method for attaching a load bearing fabric to a support structure,comprising the steps of: producing a first ring; attaching a segment ofload bearing fabric to an attachment portion of the first ring;producing a second ring including a receptacle portion adapted toreceive the attachment portion of the first ring; interfitting thesecond ring and the first ring, at least one of the second ring and thefirst ring including a stretching means for stretching the fabric as aresult of said interfitting by inserting the attachment portion of thefirst ring into the receptacle portion of the second ring; and securingthe second ring and the first ring in interfitted relation to maintainthe fabric in a stretched configuration.
 2. The method of claim 1wherein said attaching step includes the steps of: placing the fabric ina mold in a relaxed state; and molding the attachment portion of thefirst ring in situ about the fabric, whereby the first ring and thefabric become an integral combination.
 3. The method of claim 1 whereinat least one of the second ring and first ring includes integral lockingtabs, said securing step including inserting the first ring into thesecond ring until the locking tabs interlock the second ring and thefirst ring.
 4. A method for attaching a load bearing fabric to a supportstructure, comprising the steps of: producing a first ring, the firstring including an attachment portion extending outwardly from the firstring; molding the attachment portion of the first ring to a segment ofload bearing fabric; producing a second ring adapted to interfit withattachment portion of the first ring; interfitting the first ring andthe second ring, at least one of the first ring and the second ringincluding a stretching means for stretching the fabric as a result ofsaid interfitting; and; securing the first ring and the second ring ininterfitted relation to maintain the fabric in a stretchedconfiguration.
 5. The method of claim 4 wherein said molding stepincludes the steps of: placing the fabric in a mold in a relaxed state;and molding the first ring in situ about the fabric, whereby the firstring and the fabric become an integral combination.
 6. The method ofclaim 5 at least one of the first ring and second ring includes integrallocking tabs, said securing step including inserting the first ring intothe second ring until the locking tabs interlock the second ring and thefirst ring.
 7. A method for securing a load bearing fabric to a supportstructure, comprising the steps of: providing a first ring defining acentral opening and carrying a load bearing fabric extending inwardlyover the opening of the first ring, the fabric generally defining aplane, the first ring including an attachment portion extendingoutwardly from the plane, a segment of the fabric attached to theattachment portion; providing a second ring adapted to interfit with thefirst ring; interfitting the first ring and the second ring by relativemovement of the first ring and the second ring, relative movement of thefirst ring and the second ring causing a portion of the fabric to extendat an angle to the remainder of the fabric, whereby the fabric isstretched to a desired tension upon said interfitting step; and securingthe first ring and the second ring together after said interfitting stepto maintain the fabric at the desired tension.
 8. The method of claim 7wherein the second ring includes a portion extending in the directionsubstantially perpendicular to the fabric and being configured to fitwithin the opening defined by the first ring, said interfitting stepincluding the step of inserting the portion of the second ring into theopening defined by the first ring, whereby the portion of the secondring engages the fabric and forces a portion of the fabric to extend ina direction substantially perpendicular to the remainder of the fabric.9. The method of claim 8 wherein the attachment portion of the firstring is a fabric leg, and wherein the second ring defines a channeladapted to receive the fabric leg of the first ring, said interfittingstep including the step of inserting the fabric leg into the channel.10. The method of claim 9 wherein a location at which the fabric isattached to the fabric leg varies through different regions of the outerring, whereby the degree of stretch of the fabric resulting from saidinterfitting step selectively varies in different directions.
 11. Themethod of claim 10 wherein the first ring includes a trim leg extendingoutwardly from the fabric leg.
 12. The method of claim 10 wherein atleast one of the first ring and the second ring includes integrallocking tabs, said securing step including inserting the outer ring intothe inner ring until the locking tabs interlock the first ring and thesecond ring.
 13. The method of claim 12 wherein the fabric is secured tothe first ring by the step of molding the first ring in place about aperipheral portion of the fabric, whereby the fabric is encapsulated inthe first ring.